How to do thematic maping over a particular region in a layer

Hi,
I want to do thematic maping over some particular region with in a layer. Is there any filter criteria or property to to that.
I tried custom theme and gredient theme but gredient theme applies to particular layer over some column of table and custom applies some style.
I am using SQLExpress.
I have a state layer of country. and I want that when I select a particular state then the thematic maping will apply to same state. is it possible?